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<p>
Next: <a href="Host-Config.html#Host-Config" accesskey="n" rel="next">Host Config</a>, Previous: <a href="Machine-Desc.html#Machine-Desc" accesskey="p" rel="prev">Machine Desc</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Target-Description-Macros-and-Functions"></a>
<h2 class="chapter">18 Target Description Macros and Functions</h2>
<a name="index-machine-description-macros"></a>
<a name="index-target-description-macros"></a>
<a name="index-macros_002c-target-description"></a>
<a name="index-tm_002eh-macros"></a>

<p>In addition to the file <samp><var>machine</var>.md</samp>, a machine description
includes a C header file conventionally given the name
<samp><var>machine</var>.h</samp> and a C source file named <samp><var>machine</var>.c</samp>.
The header file defines numerous macros that convey the information
about the target machine that does not fit into the scheme of the
<samp>.md</samp> file.  The file <samp>tm.h</samp> should be a link to
<samp><var>machine</var>.h</samp>.  The header file <samp>config.h</samp> includes
<samp>tm.h</samp> and most compiler source files include <samp>config.h</samp>.  The
source file defines a variable <code>targetm</code>, which is a structure
containing pointers to functions and data relating to the target
machine.  <samp><var>machine</var>.c</samp> should also contain their definitions,
if they are not defined elsewhere in GCC, and other functions called
through the macros defined in the <samp>.h</samp> file.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Target-Structure.html#Target-Structure" accesskey="1">Target Structure</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">The <code>targetm</code> variable.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Driver.html#Driver" accesskey="2">Driver</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Controlling how the driver runs the compilation passes.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Run_002dtime-Target.html#Run_002dtime-Target" accesskey="3">Run-time Target</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining &lsquo;<samp>-m</samp>&rsquo; options like <samp>-m68000</samp> and <samp>-m68020</samp>.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Per_002dFunction-Data.html#Per_002dFunction-Data" accesskey="4">Per-Function Data</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining data structures for per-function information.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Storage-Layout.html#Storage-Layout" accesskey="5">Storage Layout</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining sizes and alignments of data.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Type-Layout.html#Type-Layout" accesskey="6">Type Layout</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining sizes and properties of basic user data types.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Registers.html#Registers" accesskey="7">Registers</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Naming and describing the hardware registers.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Register-Classes.html#Register-Classes" accesskey="8">Register Classes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining the classes of hardware registers.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="9">Stack and Calling</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining which way the stack grows and by how much.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Varargs.html#Varargs">Varargs</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining the varargs macros.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Trampolines.html#Trampolines">Trampolines</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Code set up at run time to enter a nested function.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Library-Calls.html#Library-Calls">Library Calls</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Controlling how library routines are implicitly called.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Addressing-Modes.html#Addressing-Modes">Addressing Modes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining addressing modes valid for memory operands.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Anchored-Addresses.html#Anchored-Addresses">Anchored Addresses</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining how <samp>-fsection-anchors</samp> should work.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Condition-Code.html#Condition-Code">Condition Code</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining how insns update the condition code.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Costs.html#Costs">Costs</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining relative costs of different operations.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Scheduling.html#Scheduling">Scheduling</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Adjusting the behavior of the instruction scheduler.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Sections.html#Sections">Sections</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Dividing storage into text, data, and other sections.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="PIC.html#PIC">PIC</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Macros for position independent code.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Assembler-Format.html#Assembler-Format">Assembler Format</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining how to write insns and pseudo-ops to output.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Debugging-Info.html#Debugging-Info">Debugging Info</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining the format of debugging output.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Floating-Point.html#Floating-Point">Floating Point</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Handling floating point for cross-compilers.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Mode-Switching.html#Mode-Switching">Mode Switching</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Insertion of mode-switching instructions.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Target-Attributes.html#Target-Attributes">Target Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining target-specific uses of <code>__attribute__</code>.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Emulated-TLS.html#Emulated-TLS">Emulated TLS</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Emulated TLS support.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="MIPS-Coprocessors.html#MIPS-Coprocessors">MIPS Coprocessors</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">MIPS coprocessor support and how to customize it.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="PCH-Target.html#PCH-Target">PCH Target</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Validity checking for precompiled headers.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="C_002b_002b-ABI.html#C_002b_002b-ABI">C++ ABI</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Controlling C++ ABI changes.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="D-Language-and-ABI.html#D-Language-and-ABI">D Language and ABI</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Controlling D ABI changes.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Named-Address-Spaces.html#Named-Address-Spaces">Named Address Spaces</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Adding support for named address spaces
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Misc.html#Misc">Misc</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Everything else.
</td></tr>
</table>

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